(1) Field of the Invention
The present invention relates to novel ordered polyacetylene compounds with side-by-side carbon chains and aligned acetylene groups in each chain and to a process for the preparation thereof. In particular, the present invention preferably relates to polydiacetylene compounds with two adjacent acetylene groups in each chain.
(2) Description of Related Art
Diacetylenes polymerize to give systems with electrical and optical properties that can potentially be exploited for a variety of important applications. These include conductive devices, electrochromic devices and biosensors. In order for polymerization to be possible, the double bonds must be aligned in very close proximity and with the correct geometry. It is also necessary for several of these chains to be so aligned. The problem of ordering these systems to give layers with uniform properties is a difficult one and current approaches involve the use of Langmuir-Blodgett troughs and thiol-metal anchors. The design and synthesis of diacetylene molecules that can self-assemble to form stable, uniform 2-dimensional systems are important areas of endeavor.
There is an increasing amount of interest in the design of planar lamellar systems containing conjugated polydiacetylene functions. These systems are known to display several interesting properties that could lend themselves to the fabrication of a variety of devices (Okada, S., et al., Acc. Chem. Res. 31:229-239 (1998); and Crooks, R. M., et al., Acc. Chem. Res. 31:219-227 (1998)). For instance, they display mechano-optical effects in which compressing the polydiacetylene layers lead to a change in color of the films (Nallicheri, R. A., et al., Macromolecules 24:517-525 (1991); and Lovell, P. A., et al., Macromolecules 31:842-849 (1998)). In other experiments, attaching a carbohydrate molecule to a polydiacetylene layer resulted in a change in color when viral particles bound to the carbohydrate (Reichert, A., et al., J. Am. Chem. Soc. 117:829-830 (1995); and Spevak, W., et al., J. Am. Chem. Soc. 115:1146-1147 (1993)). Polydiacetylene layers also demonstrate color changes in response to alterations in temperature (Chance, R. R., et al., J. Chem. Phys. 71:206-211 (1979); Rubner, M. F., et al., 20:1296-1300 (1987); and Wenzel, M., et al., J. Am. Chem. Soc. 111:6123-6127 (1989)), pH (Mino, N., et al., Langmuir 8:594-598 (1992)) and on exposure to some solvents (Nava, A. D., et al., Macromolecules 23:3055-3063 (1990)). Polyacetylene is well recognized for its high electrical conductivity. Unfortunately, it forms fibers not films, and its high insolubility and general physical intractability makes it unsuitable for many applications especially when lamellar systems are desirable. Under favorable circumstances, the use of amphophilic molecules with acetylene groups in the hydrocarbon chains leads to film formation (Lio, A., et al., Langmuir 13:6524-6432 (1997) and Werkman, P. J., et al., Langmuir 14:157-164 (1998)). However, such molecules often contain only one hydrocarbon chain and they have a tendency to form micellar systems. In order to obtain suitable films, the chains then either have to be anchored to surfaces, or Langmuir-Blodget troughs have to be employed (Charych, D. H., et al., Science 261:585-588 (1993); Berman, A., et al., Science, 269:515-518 (1995); Saito, A., et al., Langmuir, 12:3938-3944 91996); Deckert, A. A., et al., Langmuir, 10:1948-1954 (1994); and Mowery, M. D., et al., Phys. Chem. B, 101:8513-8519 (1997)). One serious problem with the ordering of actylenic thiols on gold and other metal surfaces is the difficulty in ensuring that the chains are aligned so that the alkyne groups are in a proper orientation and close enough to allow the polymerization process. This is difficult because imperfections on the metal surface of only a few atoms in dimension force adjacent chains to be at different heights, thus separating the acetylenic groups by too great a distance. A substrate-independent way of ordering alkyl chains with diacetylenic functions is therefore highly desirable. Molecular self-assembly has much promise in this area.
Phospholipids readily form stable lamellar systems. The inclusion of conjugated diacetylenic groups at the same position in each acyl chain of a phospholipid chain (FIG. 2) should give ideal self-assembling units which can be polymerized to form highly organized, stable, 2-dimensional systems containing a conducting polydiacetylene layer. Unfortunately, the synthesis of phospholipids is extremely laborious. One approach that has been tried is to use microorganisms to carry out the integration of fatty acids containing diacetylenic functions into phospholipids. Using this strategy as much as 90% integration of diacetylenic fatty acids into microbial phospholipids was obtained (Leaver, J., et al., Biochim. Biophys. Acta 727:327-334 91983)). There are some problems with this approach however; because the membrane is only two molecules thick and just surrounds the cell, the actual amount of material recovered per gram of cell mass is extremely small. In addition to this, the lipid species made by any one microorganism are extremely diverse and may include neutral, and negatively charged headgroups with different structures. It is a challenge to separate species with only one type of headgroup and, even then, there is a tremendous amount of diversity in the fatty acid species that are derived from the normal microbial metabolism. Another disadvantage stems from the fact that microorganisms contain a myriad of membrane-associated enzymatic activities that can reduce or oxidize the diacetylenic functions. Because the microorganisms make fatty acids de novo, it is very unlikely that any living system exists that will incorporate only foreign fatty acids into its membrane lipids.
Therefore, it is clear that only synthetic approaches have the potential for producing pure phospholipids or phospholipid analogs containing diacetylenic functions in the fatty acyl chains and which have a high degree of chemical integrity. Because of the difficulty in preparing phospholipids, simpler analogs which still contain the critical structural elements of phospholipids, a chiral 1,2-diacyl moiety and a polar headgroup, are desirable. Even more desirable are phospholipid analogs that have the general structure of the lipids found in bacteria that inhabit environments with extremely high temperatures or extremes of pH. The lipids of such organisms contain two transmembrane hydrocarbon chains that are linked to a headgroup at either end. In some bacteria the linkages are ether linkages but in others (Lee, J., et al., J. Am. Chem. Soc., 120:5855-5863 (1998); Jung, S., et al., J. Lipid Res. 35:1057-1065 (1994)), they are ester functions (FIG. 2). Such molecules should self-assemble to form extremely stable lamellar systems without the aid of devices such as Langmuir-Blodgett troughs. They would be excellent targets for the preparation of planar polydiacetylenic systems.